The manufacture of leather from raw hides is a multi-step process. Cattle hides are initially obtained from a slaughterhouse, and from there taken to a tannery for processing into leather. The typical stages in this multi-step process are: trimming and fleshing, soaking, hairing, liming, pickling, tanning, dyeing and finishing.
In a first step of a typical tanning process, the hides are placed into a drum which contains an acidic aqueous solution, also know as the tanning liquor. This step may be referred to as a first tanning stage. After an appropriate length of time in this tanning liquor, a basic (high pH) solution is added to the liquor in order to neutralize the acidity of the acidic aqueous solution. Then, during what is called the second tanning stage, more chemicals are added to the drum. The chemicals used in the second tanning stage may impart a bluish tinge to the hides, and thus hides that have been treated through the second tanning stage may be referred to as "wet blue hides." From the second tanning stage, the wet blue hides can be either stored for further processing or placed in a dyeing bath and then undergo further finishing.
Microbial attack of the hides can occur at many stages of the leather forming process. For example, before or immediately after being taken from a slaughterhouse, the hides may be treated with salt, which acts as a preservative while the hides are stored in the slaughterhouse, during transportation to the tannery, and during storage in the tannery. The salt must be substantially removed prior to the tanning process, and this is typically done, in part, by soaking the hides in water, optionally with agitation. Bacterial attack can occur during this soaking stage.
Also, while the hides are in, or being transported after, the second tanning stage, the hides are subject to fungal attack. For example, it is not uncommon for wet blue hides to be transported across long distances from a tannery to a leather processor, where the wet blue hides will be finished. Fugal attack of the wet blue hides is thus a concern for leather manufacturers.
Biocides are used to protect the hides from bacteria, mold and fungi. Fungal attack on leather results in unattractive black dots or other discoloration on the hides, which are very difficult to remove and/or may spoil the finish leather or wet blue hides. Aspergillus niger is a typical fungus which may attack leather. ASTM D 4576-86 (reapproved 1991) describes a test method for evaluating the mold growth resistance of blue stock leather, also called wet blue hides, that have been treated with fungicide.
U.S. Pat. No. 4,866,081 discloses that the combination of 2-(thiocyanomethylthio)-benzothiazole and 3-iodo-2-propynyl-N-carbamate, is particularly useful as a microbicidal preservative to prevent deterioration of raw materials such as dyes, pastes, lumber, leather, textiles and pulp caused by microorganisms.
There remains a need in the art for biocidal formulations which may be effectively added to water-based systems, including tanning baths for leather manufacture and aqueous inks and other coatings.